A CMP apparatus, which is a polishing apparatus, is configured to press a wafer against a polishing pad while supplying a polishing liquid (or slurry) onto the polishing pad to thereby polish the wafer. The polishing pad is supported on a polishing table, and is rotated together with the polishing table. The wafer is rotated by a polishing head, and is pressed against the rotating polishing pad by the polishing head. During polishing of the wafer, a lateral force acts on the wafer due to a friction between the wafer and the polishing pad. Thus, in order to prevent the wafer from coming off from the polishing head, the polishing head includes a retainer ring for retaining the wafer.
FIG. 39 is a schematic cross-sectional view of a conventional polishing head. A polishing head 300 includes a drive ring 302 for transmitting a torque to a retainer ring 301. The retainer ring 301 is secured to the driver ring 302. More specifically, a plurality of threaded holes 305 are formed in an upper surface of the retainer ring 301 at equal intervals. A plurality of screws 307, passing through the drive ring 302, are screwed into the threaded holes 305 of the retainer ring 301, respectively, thereby securing the retainer ring 301 to the drive ring 302.
Since the retainer ring 301 is in sliding contact with the polishing pad during polishing of a wafer W, the retainer ring 301 is gradually worn away. Therefore, the retainer ring 301 is one of consumables which must be periodically replaced. However, in order to replace the retainer ring 301, it is necessary to remove the polishing head 300 from the polishing apparatus and to disassemble the polishing head 300, because the screws 307, securing the retainer ring 301, are disposed in the polishing head 300. Therefore, it takes considerable time to replace the retainer ring 301, resulting in an increase in a downtime of the polishing apparatus.
Further, when the retainer ring 301 is fastened by the plurality of screws 307, a stress in the retainer ring 301 may vary, thus possibly causing deformation of the retainer ring 301. The retainer ring 301 has not only a function to retain the wafer W during polishing, but also a function to control an amount of rebounding of the polishing pad to thereby control a polishing rate of a peripheral portion of the wafer W. If the retainer ring 301 is deformed, the polishing rate of the peripheral portion of the wafer W may vary.